It has long been desirable to control the level of liquid particularly in fuel tanks of the type normally incorporated in aircraft. Such automatic level control systems normally will preclude overflow of the fuel tank with all the attendant disadvantages thereof such as fire hazard, waste of fuel, bad odors, and the like. Various types of systems have been developed to accomplish the desired level control such as traditional float-operated mechanisms or jet level sensor systems or diaphragm-operated valve systems. Typical level-controlled systems known to applicant are exemplified by the U.S. Pat. Nos. 2,731,029; 3,495,634; 3,561,465; and 3,732,902. While each of the systems disclosed in the prior art operate effectively under certain conditions there are various disadvantages existent associated with each of such prior-art systems.
Where a float-operated pilot valve is utilized such necessitates a relatively complex mechanical system which requires a large amount of space and complex adjustments to effect proper operation. As a result, such systems are usually expensive, large, bulky and in some cases inaccurate.
Prior-art systems known to applicant utilizing jet level sensors have been unsatisfactory in that utilization of the jet sensor has created fuel leakage into the tank even under those circumstances where a tank over pressure has dictated a shut-off of the fuel supply. Where such leakage does continue it could result in tank rupture. In addition thereto, jet level sensors have in the past been subject to unreliable operation resulting from contaminants in the fluid which tended to block the jet orifice thereby giving a false signal representative of the tank being filled with fluid when such in fact was not the case.
Diaphragm-operated valves have been subject to many of the unsatisfactory disadvantages referred to with regard to the float-operated valves above.